In general, traction motors of a totally-sealed type (totally-enclosed traction motors) are commonly used in rotating electrical machines for driving railroad vehicles from the view point of reducing maintenance. This kind of totally-enclosed traction motor principally includes a tube-shaped frame, brackets that close opposite ends of the frame, a rotor shaft supported by bearings provided in the brackets, a rotor iron core provided on the rotor shaft, a stator iron core fixed to the frame, and a stator coil secured to the stator iron core, and is configured to hermetically seal the air inside the motor.
With a totally-enclosed traction motor having such a configuration, the structure is such that the inside is hermetically sealed; therefore, the motor cannot take in outside air for cooling, which means that a measure is needed to make the frame larger and thereby increase the radiation area or the like in order to radiate inner heat to the outside. To avoid the disadvantage of becoming larger, a totally-enclosed traction motor has been proposed that uses a cooling fan as a component that separates the inside and the outside of the motor. In this traction motor, when the rotor rotates, the cooling fan fixed to the rotor agitates the air inside (inner air); therefore the inner air heated by the rotor and the stator iron core exchange heat with the cooling fan, frame, and the like, and thus the traction motor is efficiently cooled.
To design a traction motor with even greater capacity, it is necessary to cool the internal air more effectively. To this end, measures such as increasing the volume of airflow generated by the cooling fan or mounting a cooling device on the traction motor is necessary. However, with these measures, new problems occurs in that, as the volume of airflow increases, noise also increases; and in that the traction motor becomes larger due to it having a cooling device mounted thereon.
A means of solving such problem in a conventional traction motor is presented in the Patent Literature 1 below, and it involves an opening being formed in a bracket and a ventilation passage extending from the opening to the vicinity of the rotor shaft being formed on the motor-inner side of this bracket. On the main plate of the cooling fan, a plurality of blades are formed on the side surface of the bracket, and outside air is taken in through the opening by the cooling fan rotating. The outside air, which is cooling air for cooling the traction motor, flows through the ventilation passage in the bracket, over the rotor shaft, and over the blades, in that order, and is expelled through a ventilation passage formed in the frame to the outside of the motor. Thus, the radiation from the entire traction motor becomes more efficient and thus downsizing of the traction motor is achieved.